1. Field of the Invention
The present invention relates to an exhaust gas purifying apparatus of an internal combustion engine for cleaning up noxious matter in exhaust gas emitted from the internal combustion engine.
2. Related Background Art
Examples of known emission cleaning apparatus having an NO.sub.x absorption-reduction catalyst include those as described in International Laying-open Publication WO93/25806. The NO.sub.x absorption-reduction catalyst is a catalyst that temporarily absorbs nitrogen oxides NO.sub.x included in the exhaust gas when the internal combustion engine burns fuel at an air/fuel ratio leaner than the stoichiometric ratio (the leaner ratio than the stoichiometric ratio being called a lean air/fuel ratio) and that reduces the absorbed NO.sub.x into harmless matter when the engine burns fuel at the stoichiometric ratio or at an air/fuel ratio richer than the stoichiometric ratio (the richer ratio than the stoichiometric ratio being called a rich air/fuel ratio). This NO.sub.x absorption-reduction catalyst also has the function of a three way catalyst to reduce the absorbed NO.sub.x, using hydrocarbons HC and carbon monoxide CO included in the exhaust gas after combustion at the stoichiometric ratio or at a rich air/fuel ratio, as reductant. (On this occasion, HC and CO are oxidized.)